Thermal decomposition of hydrocarbons



Patented Oct. 18, 1927.

UNITED STATES PATENT .OFFICE."

GEORGE O. GURME, JR., 0! CHARLESTON, WEST VIRGINIA; ASSIGNOR TO CARBIDE AND CARBON CHEMICALS CORPORATION, A CORPORATION OF-NEW YORK. v

THERMAL DECOMPOSITION OF HYDROOARBONS.

This invention comprises a process for thermally decomposing hydrocarbons.

It is well known that hydrocarbons in general are decomposed at sufliciently elevated temperatures, and that the decomposition can be so regulated that it produces hydrocarbons of smaller molecular weight than the hydrocarbons treated. Under these conditions a considerable proportion of chemically unsaturated hydrocarbons, such as the olefines, is normally present in the decomposition product.

In an extensive-experience with processes involving the controlled-thermal decomposition of hydrocarbons, such as the process described in Patent 1,460,545 granted on July 3, 1923, to Pierre 1*). Haynes and the present applicant, various materials have been in vestigated to determine their fitness for making tubes in which to confine hydrocarbons while heating them by roducts of'combustion to temperatures as high as 1000 0. Because of its fairly good strength and resistance to oxidation at the temperatures in volved, but principally because of its cheap ness, iron was the material first chosen for the part-of the tubes which comes into contact with the combustion gases.

It was found, however, that iron exerts at 'such temperatures a powerful catalytic action on hydrocarbon vapors, promoting a reaction producing solid carbon, and the latter builds up on the walls of the tubes and soon clogs them. It was therefore necessar to line the iron tubes with copper tubing. ime no iron or copper tubing obtainable at prices permitting its industrial use for such a purpose %)as a sufliciently close approximation to a rue cylindrical surface to permit the iron tube and its copper lining accurately to interfit, a gas layer of variable thickness was present between the two tubes and interfered seriously with the heat'transfer. Furthermore the iron tubes burned out rather quickly and perforation of either the iron or the co per disabled the unit. Replacement of tu es with the attendant interference with the operation of the furnace proved to be troublesiime and expensive.

In an attempt to improve the lined tubes described above, chrome-iron was substituted for iron as the material of the jacket. This alloy was found to resist corrosion very much better than iron, but a more important 'and entirely unexpected advantage of m Drawingv Application filed January 7, 1926. Serial-No. vassaflElssuE chrome-iron was soon discovered. It was foundthat when the copper lining of a chrome-iron tube became perforated and the hydrocarbon gases came into contact with the Jacket, there was little or no deposition of carbon on the portion of the 'acket thus exposed, and no detrimental e ect on the yield of olefine hydrocarbons. Under similar conditions with iron jackets the tube would become blocked me very short time by carbon built up on the exposed iron.

Accordingly, it was indicated that unlined chrome-iron tubes could be substituted for copper-lined iron tubes with great advantage, and the unlined tubes have one into extensive useand are results. i

For use at the temperatures discussed above, the chrome-iron preferably contains upward of 20% of chromium, but the invention is not restricted to such percentages as a smaller proportion gives a useful effect, especially at lower operatingtemperatures. The best results obtained so far have been with material containing 26 to 29% chromlum. The tubes are preferably composed of a workable alloy, such as is described in the patent to Becket and McQuigg 1,454,464 dated May 8, 1923.

Seamless drawn tubing is preferred but tubes fabricated from sheet by fusion welding maybe used. The weld should be made with an alloy of approximately the same composition as the sheet forming the body of the tube. Even when this practice is followed a small amount of carbon may deposit on the weld when the tube 1s in use,-presumably because the composition of the weld is somewhat changed in the welding operation, as by oxidation of chromium. Carbon also accumulates slowly on the walls of any tube carrying heated hydrocarbon vapors in the temperature range above mentioned presumably from the baking of heavy tars formed as by-products in the cracking reaction which condense out at the temperature of operation. This carbon is readily removed by periodically passing air through the tube while heating it to a sufiicient temlperature to bring about oxidation of the cargiving exce lent 'While the invention is especially valuable p to temperatures in the vicinity 0f1900 C.', it is applicable to many processes where the temperatures and products are quite dif-- ferent. The ability of chrome-iron to resist oxidation at high temperatures is known, and the inventio'n'resides in the use of the alloy in contact with hydrocarbon material under such conditions that carbon deposition would preclude the use of commercialiron. It is intended to cover all such uses of chrome-iron in the appended claims.

I claim:

1. The process which comprises thermally decomposing hydrocarbons while the latter are in contact with an alloy consisting predominantly of chromium and'iron.

2. The process which comprises thermally decomposing hydrocarbons while the latter are in contact with, an alloy consisting predominantly of chromium and iron under 'such conditions that contact of commercial iron with the decomposing hydrocarbon would give rise toseriously interfering deposition ofcarbon. V

3. The rocess which comprises thermally decompos ng hydrocarbons while the latter are in contact with an alloy consisting predominantly of'chromium and iron and con i I and chromium tainin'g at least 20% such conditions that contact of commercial iron with the decomposing hydrocarbon would give rise to seriously interfering deposition of carbon. a

4. The process which comprises thermally decomposing hydrocarbons by confining the same at least in part. of'an alloy consisting predominantly of iron and, applying combustion gases tosaid wall to heat the hydrocarbons.

5. The process which comprises thermallyv decomposing hydrocarbons by confining the same at least in partby a wall constructed of chrome-iron contalnlng at least 20% of chromium, and applying combustion gases ,to said wall to heat the hydrocarbons; v

6. The process of thermally decomposing hydrocarbons which comprises confining the same in a chrome-iron tube resistant to oxidation at temperatures as high as 900 C., and hea ing the exterior of the tube to about said temperature by contact of combustion gases therewith.

In testimony whereof, I aflix my signature. I

GEORGE o. CURMEQJR.

by a wall constructed of chromium under 1 

